"Weinmann 600 brakes and Simplex deraileurs! This bike is gonna be at least early 70's vintage, but more probably 60's vintage."

With twelve speeds, it's closer to the eighties than sixties. Both my PKN and PFN had Weinmann brakes and simplex derailleurs (The PFN now only has the rear simplex, the PKN is almost all stock except for drilled stronglight rings and simplex retrofriction shifters), so those parts were standard on some bikes until the end of the seventies.